Mirrorback coating

ABSTRACT

A lead-free composition capable of being applied as a film and hardening to form a protective layer on the back of a mirror comprises a fluid organic resin and a corrosion inhibitor selected from the group consisting of dicyanadiamide, metal or acid salts of dicyandiamide, hydrogen cyanamide, and 2-cyanoacetamide. The organic resin may be any thermoplastic or thermosetting resin suitable for coating the reflective and other metallic layers of the mirror. Exemplary resins include alkyd resins, acrylic resins, modified alkyd resins, polyesters, urethane oils, vinyl halide polymers or copolymers, oleoresinous varnishes, nitrocellulose compositions, phenol-formaldehyde resin varnishes, and epoxy resins. Preferably, the resin is an alkyd or modified alkyd resin. The aforementioned corrosion inhibitor may be present in an amount from about 0.1 to 20 weight percent, preferably 0.5 to 10 weight percent, of the organic resin coating system. The resin system should be essentially free of lead and lead salts. To inhibit the corrosion of metallic film layers on mirrors, a mirror having a glass substrate layer and a metallic film layer thereover should be obtained, after which the fluid organic resin coating system containing the aforementioned corrosion inhibitor is aplied over the metallic film layer. The organic resin coating system is then hardened to produce the protective coating layer over the metallic layer. Other articles having metallic surfaces may also be protected by the resin system containing the novel corrosion inhibitor of the present invention.

This is a divisional of co-pending application Ser. No. 626,461 filedDec. 18, 1990, now U.S. Pat. No. 5,094,881 issued Mar. 10, 1992, whichis a continuation-in-part of Ser. No. 463,424 filed Jan. 11, 1990, nowU.S. Pat. No. 5,075,134 issued Dec. 24, 1991.

BACKGROUND OF THE INVENTION

This invention relates to a coating for use on mirror backs, and, inparticular, to a lead-free organic coating to be applied to the metallicfilm layer on the back of a mirror to protect the metallic layer andprevent corrosion thereof.

Typical mirrors are made of a glass sheet and a thin layer of a metallicfilm applied to the back of the sheet. The metallic film layer adhereddirectly to the glass is usually a film of silver, although othermetallic films may also be used, such as copper. When silver is used asthe primary reflective layer, it is commonly protected by a secondmetallic film layer of copper or some other metal.

It has long been known to employ various paints and other film-formingorganic resins as a further protective layer over a metallic film layerto protect the layer from corrosion and physical damage. Traditionally,these paints have included lead-based corrosion inhibitors, such as leadsalts. However, in recent times, both users and producers of such paintproducts have sought to eliminate the use of lead and lead compounds forhealth and environmental reasons. A recent effort in this direction isreflected in U.S. Pat. No. 4,707,405 to Evans et al. directed to use ofcyanamide salts of non-lead metals as corrosion inhibitive pigments inmirror back coatings. This patent discloses the use of such non-leadcyanamide salts as calcium cyanamide and zinc cyanamide in various typesof film-forming thermosetting or thermoplastic resins which are appliedover the silver and copper layers on the backs of mirrors. Continuingefforts have been made to produce an effective lead-free corrosioninhibiting mirror back coating to satisfy the long felt need of theindustry, but to date, no such commercial coatings have proven to be aseffective in inhibiting corrosion and overall protection as leadcontaining coatings.

Bearing in mind the problems and deficiencies of the prior art, and thelong felt need of industry, it is therefore an object of the presentinvention to provide an effective corrosion inhibiting, lead-freecoating for covering the metallic film layers on the back of a mirror.

It is another object of the present invention to provide an organicfilm-forming resin which incorporates a non-lead corrosion inhibitorwhich can be easily applied by existing techniques to mirror backs.

It is a further object of the present invention to provide a lead-freepaint for protecting thin silver and/or copper or other metallic filmlayers which imparts corrosion protection of equal to or greatereffectiveness than prior art lead containing paints.

It is yet another object of the present invention to provide aneffective process for inhibiting corrosion of metallic film layers onmirrors.

It is a further object of the present invention to provide mirror andother articles having effective protection of their metallic film layersagainst salt spray and other corrosion-causing compounds.

SUMMARY OF THE INVENTION

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which provides acomposition comprising a paint or other fluid organic resin coatingsystem capable of being applied as a film and hardened to form aprotective layer, the resin additionally containing a corrosioninhibitor selected from the group consisting of dicyandiamide and metalor acid salts thereof, hydrogen cyanamide, and 2-cyanoacetamide. Theterm "hardened" is used to mean that the coating system can be cured ifthe resins are thermosetting or dried if the resins are thermoplastic.The organic resin employed in the coating system can be anythermoplastic or thermosetting resin suitable for coating a metalliclayer such as that found on the back of a mirror. Exemplary resinsinclude alkyd resins, acrylic resins, acrylic and other modified alkydresins, polyesters, urethane oils, vinyl halide polymers or copolymers,oleoresinous varnishes, nitrocellulose compositions, phenol-formaldehyderesin varnishes, and epoxy resins. Preferably, the resin is an alkyd ormodified alkyd resin, more preferably an acrylic-alkyd copolymerphenolic resin system.

The dicyandiamide, metal or acid salt of dicyandiamide, and2-cyanoacetamide corrosion inhibitor compounds may be present in anamount from about 0.1 to 20 weight percent, preferably about 0.5 to 10weight percent, of the organic resin coating system (including resins,solvents and other additives). The hydrogen cyanamide corrosioninhibitor compound may be present in an amount from about 0.1 to 10weight percent, preferably about 0.5 to 5 weight percent, of the organicresin coating system (unless specified otherwise, all references topercentages herein are by weight). Preferably, the organic resin shouldbe essentially free of lead and lead salts, either as corrosioninhibitors or other components.

To inhibit the corrosion of metallic film layers on mirrors, a mirrorhaving a glass substrate layer and a metallic film layer thereovershould be obtained, after which the fluid organic resin coating systemcontaining one or more of the aforementioned corrosion inhibitors isapplied over the metallic film layer. The organic resin coating systemis then hardened to produce a protective coating layer over the metalliclayer.

The preferred mirror article contains, in sequence, the glass substrate,the metallic film layer(s) which may be silver and/or copper or someother metal, and the hardened organic resin system as described above.Preferably, the mirror has a thin layer of silver film attached directlyto the glass layer as the reflective layer, a thin protective layer of acopper film over the silver layer, and the hardened coating systemdescribed above directly over the copper film layer as the primarycorrosion inhibitor layer. Other articles having metallic surfaces maybe protected by the non-lead corrosion inhibitor-containing resinsystems described above as well.

DETAILED DESCRIPTION OF THE INVENTION

The mirrors and metallic film layers on which the coating of the presentinvention has been found to be particularly useful are those in whichone or more layers of silver and/or copper films have been applied to aglass substrate, although the coating may also be useful over filmlayers of other metals as well. Preferably, the mirror consists of asubstrate layer of glass and a layer of reflective silver or copper filmapplied to the rear surface of the glass. If a silver film is applieddirectly to the glass, it is common to apply a second film layer ofcopper over the silver to provide protection against corrosion andphysical damage to the silver layer. Such metallic film layers arerelatively thin and on the order of approximately 700 angstroms for thesilver layer and approximately 220 angstroms for the copper layer.

Such mirrors may be made by any of the known processes in the prior art.The glass surface to which the metallic film layer is to be applied isusually lightly polished and cleaned and thereafter sensitized with anaqueous stannous chloride solution. The silver film layer may bedeposited on the sensitized glass surface by one of many methods such asthat described in U.S. Pat. No. 4,737,188 to Bahls, the disclosure ofwhich is hereby incorporated by reference, in which an N-methylglucaminereducer is utilized with ammoniacal silver nitrate and a strong basesuch as sodium hydroxide in aqueous solutions sprayed on and combined atthe sensitized glass surface to deposit the silver film. Thereafter, acopper film may be applied to and over the silver film by any one of avariety of prior art procedures such as a galvanic process whichutilizes aqueous suspensions of iron and copper powder or by thedisproportionation of cuprous ions on the silver surface. The latterprocess is described in U.S. Pat. No. 3,963,842 to Sivertz et al, thedisclosure of which is hereby incorporated by reference. In suchprocess, a cupric tetraammonium sulfate solution is reduced bycombination with hydroxylamine sulfate and thereafter reacted with anactivator-modifier such as a mixture of citric acid or ethylene diamineand H₂ SO₄ to form a copper film on the silvered surface.

The coating of the present invention to be applied over the copper,silver or other metallic film layer is based on any suitablethermosetting or thermoplastic organic film-forming resin. Thethermosetting resins contemplated in use in the present invention arethose that require heat to effect curing, such as by infrared heating,although room temperature air drying resins are also included.

Suitable resins include alkyd resins, acrylic resins, polyesters,urethane oils, vinyl halide polymers or copolymers, oleoresinousvarnishes, nitrocellulose compositions, phenol-formaldehyde resinvarnishes, epoxy resins, or combinations of such resins. Preferably, theresins employed in the present invention are alkyd or modified alkydresins such as acrylic-alkyd copolymers in combination with a solvent,and other additives such as a pigment, if desired, to produce a resincoating system. Such alkyd resin systems may be modified with acrylics,urethanes and polyurethanes, phenolics, and combinations of the above.More preferably, the resins may be acrylic-alkyd copolymers and phenolicresins in combination. Amino crosslinking agents such asmelamine-formaldehyde resins and/or urea-formaldehyde resins may beincluded in the modified alkyd or other resin system to make the systemheat-curable. Alternatively, metal driers can be employed in the systemto make it air drying.

The resin system of the present invention should employ a binder resinwhich casts a suitable film and provides good adhesion to and over theaforementioned metallic film layer(s). The system may employ a suitablesolvent of the type normally employed in the particular resin system.For example, in the preferred alkyd and modified alkyd resin systems ofthe present invention, an ester such as propylene glycol monomethylether acetate, butyl acetate or isobutyl acetate may be employed.Preferably, the alkyd or modified alkyd resins comprise 20 to 50 percentby weight of the system, more preferably 20 to 35 weight percent. Thesolvents or solvent blends employed in this system are preferably 20 to35 percent by weight of the system. Additives normally employed in resincoating systems for this type of application may also be added inaddition to the resin and solvent, for example, pigments (where it isdesired to impart a color) and inert fillers or extenders such asbarytes or calcium carbonate; flow additives; anti-settling agents tosupport any dense pigment particles; catalysts such as blocked orunblocked acids (where a thermosetting resin is employed); surfaceactive agents; antiskinning agents such as methyl ethyl ketoxime; andadditives for other purposes.

The aforementioned resin systems are by themselves fully hardenable toform a film over a metallic film layer. To impart effective corrosionresistance for the metallic film layer, the present inventionspecifically contemplates the use of a non-lead compound selected fromthe group consisting of dicyandiamide (also known as "cyanoguanidine"),metal or acid salts thereof, hydrogen cyanamide, 2-cyanoacetamide, orcombinations of the above. Unless specified otherwise, references hereinto use of dicyandiamide shall also apply to metal or acid salts ofdicyandiamide, in connection with the corrosion inhibitor of the presentinvention. The dicyandiamide and 2-cyanoacetamide corrosion inhibitorsmay be employed in a range from about 0.01 to about 20% by weight of theresin coating system, although the range from about 0.1 to about 10% ispreferred. More preferably, a range from about 0.5-1% to about 5% isemployed for maximum effectiveness. At the higher amounts, particularlyabove 10%, the dicyandiamide becomes particularly susceptible toreaction with water, for example, any moisture present in theenvironment. If such higher amounts of the dicyandiamide are employed inthe resin coating system of the present invention, it is preferred thatan additional water or moisture proof coating be applied over thehardened resin coating. The 2-cyanoacetamide has also not been found tohave enhanced effectiveness in amounts greater than 10-20% by weight ofthe total resin system.

The hydrogen cyanamide corrosion inhibitor may be employed in a rangefrom about 0.01 to about 10% by weight of the resin coating system,although the range from about 0.1 t o about 5% is preferred. Morepreferably, a range from about 0.5-1% to about 2.5% by weight isemployed for maximum effectiveness.

The dicyandiamide, hydrogen cyanamide, and 2-cyanoacetamide corrosioninhibitors of the present invention may be blended with the resin systemby comminuting them into fine particles, preferably from 10 to 20microns or less in size. It has been found that when the small sizeparticles are employed, a lower overall weight percentage of theinhibitor is needed to achieve a desired level of corrosion protection,since the smaller particle size can be dispersed throughout the resin toa greater extent to provide the necessary protection. Alternatively, thecorrosion inhibitor may be dissolved in a suitable solvent and dispersedand blended into the resin system. The dicyandiamide, cyanamide and2-cyanoacetamide are believed to be substantially unreacted in theblended, fluid resin system and available for reaction during or afterapplication to the metallic surface.

While not wishing to be limited by theory, it is thought that thedicyandiamide and other non-lead corrosion inhibitor compounds disclosedherein react in the present system to: 1) passivate the metallic film onwhich it is applied, for example, a copper film, and create a complexwith the metal to reduce corrosion; 2) increase the adhesion of themetal film, such as copper, to the cured resin; or 3) a combination of 1and 2 above. The dicyandiamide, cyanamide and/or 2-cyanoacetamidecorrosion inhibitors are incorporated instead of utilizing conventionallead based pigments, such as lead salts, employed in the past. However,other corrosion inhibitors may be used in conjunction with thedicyandiamide, cyanamide and/or 2-cyanoacetamide, such as zinc oxide, toprovide a desired degree of protection in a specific application. Ifdesired, low amounts of leaded materials which comply with environmentallaws and regulations may be added to the resin system. Preferably, theblended resin system to be applied over the aforementioned metallicfilms is completely free of lead to comply more easily withenvironmental laws and regulations in its manufacturing and use.

The blended resin system employing the non-lead corrosion inhibitors ofthe present invention is applied to the metallic layers on the mirrorbacks by conventional processes, such as air or airless spraying(preferably the latter), roller coating, or curtain coating.Thermosetting resin systems such as the aforementioned preferred alkydor modified alkyd resin systems may be dried by infrared heating,typical conditions being five minutes heating time with an exit filmtemperature of about 250° F. (120° C.). The thickness of the dried resinfilm layer may be up to 0.002 in. (51 microns) thick, although it ispreferred that the film thickness be from about 0.001 to 0.0015 in. (25to 38 microns) in thickness. Where thicker coatings are desired,multiple layers of the coating may be applied. The use of the thinlayers described above enables the applied resin system to be quicklydried to a hardened layer without causing bubbles or other defects. Theresin system incorporating the dicyandiamide, cyanamide and/or2-cyanoacetamide corrosion inhibitors of the present invention providesgood protection to the edges of the mirror metallic film layers, atwhich location corrosion usually commences. Mirror edge corrosion (alsoknown as "black edge") can occur because of moisture present inbathrooms or other high humidity environments. Other causes include theuse of certain adhesives in which a component (for example, acetic acidin silicone based adhesives) can attack the resin coating layer andmetallic film. Also, where the edges of the mirrors are bevelled orpolished with an abrasive, abrasive coolant having a high pH level canremain on the edge and attack the paint and metallic film layers of themirror.

In addition to providing good corrosion protection, the resin coatingsystem employing the dicyandiamide, cyanamide and/or 2-cyanoacetamidecorrosion inhibitors of the present invention should be able to providea smooth finish having a good appearance, and, if the mirror is latercut or otherwise handled, should prevent chipping of the resin paint atthe mirror edges.

The following non-limiting examples are provided to illustrate resinsystems employing dicyandiamide, cyanamide and/or 2-cyanoacetamidecorrosion inhibitors of the present invention.

EXAMPLES

A series of glass panels were cleaned, sensitized, and coated withsuccessive layers of a silver film and a copper film according to theprocesses described above. The resulting silver film layer wasapproximately 700 angstroms thick and the resulting copper film toplayer was approximately 220 angstroms thick.

I. Dicyandiamide

To test the effect of dicyandiamide as a corrosion inhibitor, mirrorback paint coatings to be applied over the silver and copper layers wereprepared by mixing starting compositions A and B as follows (componentsreported in parts by weight):

    ______________________________________                                                                Composition:                                          Component                 A      B                                            ______________________________________                                        acrylic-alkyd copolymer   20.4   36                                           (Freeman Chemical Chempol 13-1214)                                            phenolic resin solution (44.5% Union                                                                    10.9   --                                           Carbide Corp. Ucar CK2400; 22.2%                                              mineral spirits; 22.2% butyl alcohol;                                         11.1% xylene)                                                                 carbon black (Pfizer Superjet LB-1011)                                                                  0.8    --                                           barium sulfate            27.3   --                                           (Thompson Weiman Barimite XF)                                                 6% cobalt naphthenate (Celanese Corp.)                                                                  0.18   --                                           6% manganese naphthenate (Mooney Chem.)                                                                 0.14   --                                           methyl ethyl ketoxime     0.8    --                                           (Tenneco Chemical Exkin 2)                                                    propylene glycol monomethyl ether                                                                       13.6   28                                           acetate (Dow Chemical PM acetate)                                             xylene                    8.5    --                                           talc (Cyprus Minerals Mistron                                                                           17.0   --                                           Monomix)                                                                      dicyandiamide             --     36                                           ______________________________________                                    

The components of each of the compositions A and B were dispersed bygrinding to a particle size of 6 on the Hegman Scale.

In the course of testing the dicyandiamide corrosion inhibitor of thepresent invention, compositions A and B were combined in amounts of 100g and 120 g, respectively, along with 20 g of the acrylic acid copolymerand 10 g of the phenolic resin solution to produce resin coating systemsample no. 1 containing 17.3% dicyandiamide. Six additional differentresin systems were prepared by combining different amounts ofcompositions A and B to produce resin system samples 2 through 7containing dicyandiamide in the following respective amounts: 8.6%,4.3%, 2.9%, 0.8%, 0.12% and 0.015%. Additional amounts of theaforementioned resins and pigments were added as necessary to maintainan approximately equal ratio of pigment to resin throughout thedifferent resin systems. A control sample resin system was prepared inthe same pigment to resin ratio, but without any dicyandiamide. Table Ishows the compositions of the aforementioned samples.

The eight different liquid resin coating systems (seven withdicyandiamide corrosion inhibitor, one control) were applied to thecopper layer on the backs of the aforementioned mirrored glass samplesusing a draw down bar and thereafter subjected to infrared drying atabout 250° F. (120° C.) for approximately five (5) minutes until curedto a hardened film layer of approximately 0.001 in. (25 microns)thickness.

The coated mirror samples were then subjected to a corrosion test in a20% salt spray environment for 300 hours pursuant to Federalspecification DD-M-00411 c. Following completion of the test the mirrorswere evaluated for corrosion by noting the appearance of the silver (andother film layers) from the front of the mirror.

                                      TABLE I                                     __________________________________________________________________________    (Amounts reported in parts by weight)                                                        Sample Nos.:                                                                  1  2   3   4   5   6   7   Control                             __________________________________________________________________________    Composition A  100.0                                                                            100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                               Composition B  120.0                                                                            60.0                                                                              30.0                                                                              20.0                                                                               5.0                                                                               0.8                                                                               0.11                                                                             --                                  Acrylic-alkyd copolymer                                                                       20.0                                                                            41.6                                                                              52.4                                                                              56.0                                                                              61.4                                                                              62.9                                                                              63.16                                                                             63.2                                Phenolic resin solution                                                                       10.0                                                                            10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                Propylene glycol monomethyl                                                                  -- 16.8                                                                              25.2                                                                              28.0                                                                              32.2                                                                               33.37                                                                            33.58                                                                             33.6                                ether acetate                                                                 Talc           -- 21.6                                                                              32.4                                                                              36.0                                                                              41.4                                                                              42.9                                                                              43.16                                                                             43.2                                __________________________________________________________________________

                  TABLE II                                                        ______________________________________                                                Wt. %       Black     Density                                                                              Spot                                     Sample  Dicyandiamide                                                                             Edge (mm) of Spots                                                                             Size                                     ______________________________________                                        1       17.3        total failure (clear glass)                               2       8.6           1 mm    dense  1-2 mm                                   3       4.3         0.3 mm    medium pin points                               4       2.9         0.3 mm    very few                                                                             pin points                               5       0.8         0.3 mm    medium faint pin                                                                     points                                   6       0.12        0.3 mm    medium large spots                              7       0.015       total failure (film still attached)                       8 (Control)                                                                           0.0         total failure (clear glass)                               ______________________________________                                    

Both the control sample and the sample having the 17.3%dicyandiamide-containing resin showed complete failure of the metal filmlayers as they and the resin film layer had peeled off the glass layer.The samples having the 2.9% and 0.8% dicyandiamide resin had very goodappearance with only fine pinpoints visible on the silver film layer andminimal corrosion at the mirror edges. The samples having the 8.6%,4.3%, 0.12% and 0.015% dicyandiamide resin showed corrosion between thetwo extremes described above. The results of the salt spray test areshown in Table II. Except for the sample having the 17.3% dicyandiamideresin, the presence of dicyandiamide in the resin system resulted inmarked improvement in corrosion testing, as compared to the controlsample having no dicyandiamide. This is best shown by the reduced edgecreep on the mirror samples. It is believed that the failure of thesample having the 17.3% dicyandiamide resin resulted from reaction ofthe dicyandiamide with water, which reaction may be prevented by use ofa water or moisture proof top coat over the resin system of the presentinvention.

II. Cyanamide

To test the effect of hydrogen cyanamide as a corrosion inhibitor,mirror back paint coatings to be applied over the silver and copperlayers were prepared by mixing starting compositions AA and BB asfollows (components reported in parts by weight):

    ______________________________________                                                               Composition:                                           Component                AA     BB                                            ______________________________________                                        acrylic-alkyd copolymer  39.1   37.2                                          (Freeman Chemical Chempol 13-1214)                                            phenolic resin solution (44.5% Union                                                                   9.9    9.4                                           Carbide Corp. Ucar CK2400; 22.2%                                              mineral spirits; 22.2% butyl alcohol;                                         11.1% xylene)                                                                 carbon black (Pfizer Superjet LB-1011)                                                                 0.6    0.6                                           barium sulfate           20.0   19.0                                          (Thompson Weiman Barimite XF)                                                 6% cobalt naphthenate (Mooney Chem.)                                                                   0.09   0.09                                          6% manganese naphthenate (Mooney Chem.)                                                                0.07   0.065                                         methyl ethyl ketoxime    0.41   0.37                                          (Cosan Chemical Coskin M)                                                     butyl acetate            10.4   10.9                                          xylene                   7.0    7.2                                           talc                     12.5   11.9                                          hydrogen cyanamide       --     3.37                                          ______________________________________                                    

The components of each of the compositions AA and BB were dispersed bygrinding to a particle size of 6 to 6.5 on the Hegman Scale. Sampleswere prepared by combining compositions AA and BB in in varying amountsas shown in Table III to produce three different levels of hydrogencyandiamide-containing resin in the following amounts: 3.4%, 1.7% and0.84% by weight. A control sample containing no hydrogen cyanamide wasmade from straight composition AA.

Resin coating system samples nos. 9-12 were applied to the copper layerson the backs of the aforementioned mirrored glass samples using a drawdown bar to a thickness of 0.0014 in. (36 microns) and thereaftersubjected to infrared drying at about 250° F. (120° C.) forapproximately two (2) minutes until cured to a hardened film layer.

The coated mirror samples were then subjected to a corrosion test basedon Federal specification DD-M-00411 c in a 20% salt spray environmentfor 300 hours. Following completion of the test the mirrors wereevaluated for corrosion by noting the appearance of the silver (andother film layers) from the front of the mirror. The results are notedin Table IV.

                  TABLE III                                                       ______________________________________                                        (Amounts reported in parts by weight)                                                   Wt. %                                                                         Cyanamide    AA     BB                                              ______________________________________                                        Sample No. 9                                                                              3.4            --     100                                         Sample No. 10                                                                             1.7            50     50                                          Sample No. 11                                                                              0.84          75     25                                          Sample No. 12                                                                             --             100    --                                          (Control)                                                                     ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                                  Wt.%                                                                          Cyanamide Observations                                              ______________________________________                                        Sample No. 9                                                                              3.4         80% failure of coating                                Sample No. 10                                                                             1.7         6-9 mm edge corrosion/                                                        0.6-2.5 mm spots                                      Sample No. 11                                                                              0.84       2 mm edge corrosion/                                                          0.3 mm spots                                          Sample No. 12                                                                             --          100% failure of                                       (Control)               coating                                               ______________________________________                                    

With the exception of the sample containing 3.4% cyanamide, the presenceof the cyanamide in the resin system resulted in improvement incorrosion testing on a mirror as compared to the control sample havingno cyanamide. It is believed that the failure of the sample having the3.4% cyanamide resulted from a presence of an excess amount of thecompound required in this particular resin formulation and applicationwhich reacted unfavorably in the salt water environment of testing.Protection of the hardened resin coating by a waterproof top coat mayalleviate this.

III. Cyanoacetamide

To test the effect of 2-cyanoacetamide as a corrosion inhibitor, mirrorback paint coatings to be applied over the silver and copper layers wereprepared by mixing starting compositions EE and FF as follows(components reported in parts by weight):

    ______________________________________                                                               Composition:                                           Component                EE      FF                                           ______________________________________                                        acrylic-alkyd copolymer  39.5    36.0                                         (Freeman Chemical Chempol 13-1214)                                            phenolic resin solution (44.5% Union                                                                   9.9     9.1                                          Carbide Corp. Ucar CK2400; 22.2%                                              mineral spirits; 22.2% butyl alcohol;                                         11.1% xylene)                                                                 carbon black (Pfizer Superjet LB-1011)                                                                 0.6     0.5                                          barium sulfate           20.2    18.4                                         (Thompson Weiman Barimite XF)                                                 6% cobalt naphthenate (Mooney Chem.)                                                                   0.08    0.08                                         6% manganese naphthenate (Mooney Chem.)                                                                0.06    0.06                                         methyl ethyl ketoxime    0.41    0.36                                         (Cosan Chemical Coskin M)                                                     butyl acetate            9.9     12.4                                         xylene                   6.6     8.2                                          talc                     12.6    11.5                                         2-cyanoacetamide         --      3.3                                          ______________________________________                                    

The components of each of the compositions EE and FF were dispersed bygrinding to a particle size of 6 to 6.5 on the Hegman Scale. Sampleswere prepared by combining compositions EE and FF in in varying amountsas shown in Table V to produce three different levels of2-cyanoacetamide containing resin in the following amounts: 3.3%, 1.7%and 0.83% by weight. A first control sample containing no2-cyanoacetamide was made from straight composition EE. A second controlsample was made by adding and mixing 2.4 g of dicyandiamide in 9.6 g ofdimethylformamide to 300 g of composition EE so that it contained 0.8%by weight dicyandiamide.

Resin coating system samples nos. 13-17 were applied to the copperlayers on the backs of the aforementioned mirrored glass samples using adraw down bar to a thickness of 0.0014 in. (36 microns) and thereaftersubjected to infrared drying at about 250° F. (120° C.) forapproximately two (2) minutes until cured to a hardened film layer.

The coated mirror samples were then subjected to a corrosion test basedon Federal specification DD-M-00411 c in a 20% salt spray environmentfor 300 hours. Following completion of the test the mirrors wereevaluated for corrosion by noting the appearance of the silver (andother film layers) from the front of the mirror. The results are notedin Table VI.

                  TABLE V                                                         ______________________________________                                        (Amounts reported in parts by weight)                                                      Wt. %                                                                         2-Cyanoacetamide                                                                          EE      FF                                           ______________________________________                                        Sample No. 13  3.3           --      100                                      Sample No. 14  1.7           50      50                                       Sample No. 15   0.83         75      25                                       Sample No. 16  --            100     --                                       (Control)                                                                     Sample No. 17  --                                                             (Control-0.8% dicyan.)                                                        ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                                 Wt. %                                                                         Cyanoacetamide                                                                           Observations                                              ______________________________________                                        Sample No. 13                                                                            3.3          1-2 mm edge corrosion                                 Sample No. 14                                                                            1.7          1-2 mm edge corrosion                                 Sample No. 15                                                                             0.83        2-19 mm edge corrosion                                                        0.3 mm spot                                           Sample No. 16                                                                            --           100% failure of                                       (Control)               coating                                               Sample No. 17                                                                            --           1 mm edge corrosion                                   (Control - 0.8%                                                               dicyan.)                                                                      ______________________________________                                    

The presence of the higher tested amounts of 2-cyanoacetamide in theresin system applied on a mirror back resulted in improved performancein corrosion testing as compared to the control sample having no2-cyanoacetamide (no.16).

The aforementioned examples of resin systems including thedicyandiamide, hydrogen cyanamide and/or 2-cyanoacetamide corrosioninhibitors of the present invention may be further modified, forexample, by including other pigments such as zinc oxide or titaniumdioxide in part replacement for the talc, or by using additional resinin part replacement for the pigments to achieve better corrosionresistance. In addition to protection of film layers of mirrors, asdescribed above, the resins containing the dicyandiamide, hydrogencyanamide and/or 2-cyanoacetamide corrosion inhibitors of the presentinvention may be applied to and over metallic surface layers, such ascopper, copper-based alloys, silver, or silver based alloys of otherarticles to provide enhanced corrosion protection.

While the invention has been described with reference to specificembodiments, it will be recognized by those skilled in the art thatvariations are possible without departing from the spirit and scope ofthe invention, and that it is intended to cover all changes andmodifications of the invention disclosed herein for the purposes ofillustration which do not constitute departure from the spirit and scopeof the invention.

Having thus described the invention, what is claimed is:
 1. An articlehaving a metallic surface and a protective coating layer over themetallic surface made from a hardened organic resin coating system,selected from the group consisting of alkyd resins, modified alkydresins, acrylic resins, melamine formaldehyde resins, urea formaldehyderesins, and combinations of the above, incorporating a corrosioninhibitor selected from the group consisting of hydrogen cyanamide and2-cyanoacetamide.
 2. The article of claim 1 wherein said metallicsurface is made of copper or a copper based alloy.
 3. The article ofclaim 1 wherein said metallic surface is made of silver or a silverbased alloy.
 4. The article of claim 1 wherein said corrosion inhibitoris present in an amount of about 0.1 to 10 weight percent of saidorganic resin coating system.
 5. The article of claim 1 wherein saidcorrosion inhibitor is present in an amount of about 0.1 to 10 weightpercent of said organic resin coating system.
 6. The article of claim 5wherein said organic resin coating system is selected from the groupconsisting of alkyd resins and modified alkyd resins.
 7. The article ofclaim 5 wherein said corrosion inhibitor is hydrogen cyanamide.
 8. Thearticle of claim 5 wherein said corrosion inhibitor is 2-cyanoacetamide.9. The article of claim 5 wherein said corrosion inhibitor is2-cyanoacetamide.
 10. An article having a metallic surface made of ametal selected from the group consisting of silver, copper, and alloysof silver and copper, and a cured protective coating layer over themetallic surface made from an essentially lead-free, organic resincoating system containing a corrosion inhibitor in an amount of about0.1 to 20 weight percent selected from the group consisting of hydrogencyanamide and 2-cyanoacetamide, said organic resin coating system beingselected from the group consisting of alkyd resins, modified alkydresins, acrylic resins, melamine formaldehyde resins, urea formaldehyderesins, and combinations thereof.
 11. The article of claim 10 whereinsaid corrosion inhibitor is present in an amount of about 0.5 to 5weight percent of said organic resin coating system.
 12. The article ofclaim 10 wherein said corrosion inhibitor is hydrogen cyanamide.
 13. Amirror comprising, in sequence, a glass substrate layer, a metallic filmlayer attached to the glass layer, and a protective coating layerattached to the metal layer made from a hardened organic resin coatingsystem incorporating a corrosion inhibitor selected from the groupconsisting of hydrogen cyanamide and 2-cyanoacetamide.
 14. The mirror ofclaim 13 wherein said resin system includes an organic resin selectedfrom the group consisting of alkyd resins, acrylic resins, modifiedalkyd resins, polyesters, urethane oils, vinyl halide polymers orcopolymers, oleoresinous varnishes, nitrocellulose compositions,phenolformaldehyde resin varnishes, melamine formaldehyde resins, ureaformaldehyde resins, epoxy resins, and combinations of the above. 15.The mirror of claim 13 wherein said corrosion inhibitor is present in anamount of about 0.1 to 20% weight percent of said organic resin coatingsystem.
 16. The mirror of claim 13 wherein said metallic film layercomprises one or more layers of a metal selected from the groupconsisting of silver and copper.
 17. The mirror of claim 13 wherein saidhardened coating layer is attached to a copper film layer.
 18. Themirror of claim 13 wherein said hardened coating layer is attached to asilver film layer.
 19. The mirror of claim 13 wherein said hardenedcoating layer is lead-free.
 20. The mirror of claim 13 wherein saidcorrosion inhibitor is present in an amount of about 0.5 to 5 weightpercent of said organic resin coating system.
 21. The mirror of claim 13wherein said corrosion inhibitor is present in an amount of about 0.1 to10 weight percent of said organic resin coating system.
 22. The mirrorof claim 21 wherein said organic resin coating system is selected fromthe group consisting of alkyd resins, modified alkyd resins, acrylicresins, melamine formaldehyde resins, urea formaldehyde resins, andcombinations thereof.
 23. The mirror of claim 21 wherein said corrosioninhibitor is hydrogen cyanamide.
 24. The mirror of claim 21 wherein saidcorrosion inhibitor is 2-cyanoacetamide.
 25. A mirror comprising, insequence, a glass substrate layer, metallic film layer attached to theglass layer, said metallic film layer comprising one or more layers of ametal selected from the group consisting of silver and copper, and acured protective coating layer attached to the metal layer made from anessentially lead-free, organic resin coating system containing acorrosion inhibitor in an amount of about 0.1 to 20 weight percentselected from the group consisting of hydrogen cyanamide and2-cyanoacetamide, said organic resin coating system being selected fromthe group consisting of alkyd resins, modified alkyd resins, acrylicresins, melamine formaldehyde resins, urea formaldehyde resins, andcombinations thereof.
 26. The mirror of claim 25 wherein said corrosioninhibitor is present in an amount of about 0.5 to 5 weight percent ofsaid organic resin coating system.
 27. The mirror of claim 25 whereinsaid corrosion inhibitor is hydrogen cyanamide.
 28. The mirror of claim25 wherein said corrosion inhibitor is 2-cyanoacetamide.